The present invention relates to the use of variable domains of camelid heavy-chain antibodies (VHH domains) di-rectedagainst an intracellular target and having an isoelectric point of at least8.5, for targeting said intracellular target or for thepreparation of a peptide vector. Particularly, it concerns VHH domainsdirected against a glial fibrillary acidic protein and usesthereof for preparing therapeutic or diagnostic agents.